This invention generally relates to a method for non-destructively measuring the wall thickness or core shift of dual wall structures having a single crystal or oriented polycrystalline structure. More particularly, this invention relates to using ultrasonic wave propagation and reflection to determine the thickness of dual wall structures and to determine core shift when knowledge of the material sound velocity is not necessary.
United States Patent Application Publication No. 2004/0261532 discloses the principle of measuring the thickness of a solid injection molded layered material by the use of multiple transducers. This publication does not disclose how to determine core dimensions, or how to obtain thickness data from a material of unknown sound velocity.
U.S. Pat. No. 5,907,098 discloses an apparatus and method to determine the thickness and defects for an object, such as a turbine blade, by vibrating the turbine blade. This patent does not disclose how to determining dual wall thickness or hollow core dimensions from a core or material of unknown sound velocity.
Advances in turbine blade design have led to internal geometries, such as dual wall construction having hidden wall thicknesses that conventional ultrasonic wall thickness measurement techniques cannot efficiently measure. This is because the knowledge of material sound velocity is needed in the prior art.
Computer axial tomography (CAT) scanning is currently the most prevalent practice used to inspect dual wall turbine blades in the prior art. This inspection technique includes the determination of the thickness of dual walled turbine blades and is expensive and requires use of specialized and costly equipment. In the prior art, a single wall turbine blade or single wall workpiece to be analyzed may typically be immersed into a water tank for ultrasonic evaluation by an immersion transducer. Typically, an immersion transducer may be designed to operate in a liquid environment, such as a water tank. The immersion transducer may not usually contact the workpiece. The immersion transducer may send and receive ultrasonic waves via water as a couplant.
As can be seen, there is a need for improved apparatus and methods to analyze dual walled structures, such as turbine blades at a cost of less than what can be done using CT technology. Furthermore, there is a need to improve product development cycle time and reduce field failures due to thin walls or core breakout.